Hillary supporters, dubbed Pantsuit Nation, are not happy the operator of a Facebook group is cashing out.Getty Images; EPA

Members of an underground pro-Hillary Clinton Facebook group are livid after the operator announced she would be cashing in on the page with a book deal.

News that Pantsuit Nation founder Libby Chamberlain would be putting out a tome next May based on comments from the popular page — which has some 4 million members — prompted a flood of angry comments calling the Brooklin, Maine, woman a sellout.

“Libby you should be ashamed. This is a disgusting betrayal of trust and using others’ stories to make money and gain fame,” wrote a Pantsuit Nation member named Jamie Bryant, who describes herself on Twitter as a “radical feminist bitch.”

The Pantsuit Nation Facebook page was started last October as a place where enthusiastic supporters of the Democratic presidential nominee could gather and talk about their favorite candidate.

The page grew by millions in just weeks, and by Election Day, Hillary-loving users posted pictures of themselves in pantsuits going to the polls, hopefully to elect the first female president.

Members were devastated when Clinton lost to GOP nominee Donald Trump and flocked to the page to commiserate.

Clinton herself even seemed to give a shoutout to the page during her concession speech, when she thanked “private Facebook sites” for supporting her campaign.

But when Chamberlain, a part-time school worker with two kids, announced Monday that she was doing the book — which she called “a permanent, beautiful, holdable, snuggle-in-bed-able, dogear-able, shareable, tearstainable book. Your voices. Your stories” — many users felt stabbed in the back.

“Libby, this is a betrayal of safe space,” group member Ellen Byrne wrote. “You can’t invite people to share intimate thoughts . . . then summarily, as an individual, change those terms. Something sacred has happened on this page and I don’t believe it belongs.”

Some were particularly upset that in her announcement, Chamberlain bragged the book would be on “nightstands and coffee tables all around the world.”

Member Ada Y. Sheng wrote: “Can I point out the pathetic irony that 4 million people drawn together behind the incredibly strong and smart woman that we hoped would be the leader of the free world is now . . . going to produce a coffee table book. Seriously?”

Libby ChamberlainTwitter

Others went on Twitter to mock Chamberlain’s book plans.

“5 Million members of Pantsuit Nation and the best they can come up with is another edition of Chicken Soup for the Soul,” wrote user Ijeoma Oluo.